Recently, high integration and fineness have been promoted in a device process, and the integrity of a device active region in a surface layer and the improvement of gettering ability to capture impurities such as metals caused by increase of bulk micro defects (BMD) formed by oxide precipitates (oxygen precipitation nuclei) in a bulk have been required of a silicon wafer.
In response to these requirements, various approaches have been attempted. For example, in order to eliminate defects (mainly grown-in defects) on a wafer surface, it has been performed that a wafer obtained by the Czochralski method (CZ method) is subjected to a high temperature heat treatment in an atmosphere of an argon gas or a hydrogen gas, or a mixture gas atmosphere thereof at 1100–1350° C. for 10–600 minutes.
However, in the case that a silicon wafer having a large diameter of 200 mm or 300 mm or more is subjected to the high temperature heat treatment as described above, slip dislocations, which penetrate a wafer from its back side to the front, are remarkably generated. Such slip dislocations are grown further in a device process, they cause a failure in a device process, and they have been one of factors of lowering a yield.
Moreover, in the case that a silicon wafer having a large diameter of 300 mm or more is subjected to the high temperature heat treatment, as compared to the case that a silicon wafer having a diameter of 200 mm is subjected to the high temperature heat treatment, the generation of slip dislocations is remarkably increased, these slip dislocations have penetrated a annealed wafer from its back side to the front, and have been detected by a visual inspection or a particle counter. Namely, in the above heat treatment process, it was impossible to eliminate crystal defects in a wafer surface and suppress slip dislocations at the same time.